1. Field of the Invention
The present invention relates to a laser oscillator for use in laser machining, medical treatment, illumination, communication, etc. and in particular to a laser oscillator having a function of decomposing organic matter such as oil mist in the oscillator by photocatalysis, to reduce contamination of optical components by the organic matter.
2. Description of Related Art
In general, there exists vaporized organic matter such as oil mist in an ambience around optical components of a laser oscillator for various causes. The vaporized organic matter is congealed and adhered to surfaces of the optical components which are cooled forcedly, and the congealed organic matter absorbs a laser beam to lower an output power of the laser beam and generates heat to deteriorate or distort the optical components to lower quality of the laser beam.
FIG. 4 is a partial cross-section of a gas laser oscillator in the vicinity of an optical component for explaining the above phenomenon in a case of gas laser. In FIG. 4, a reference numeral 2 denotes an electric discharge tube and a reference numeral 4 denotes one of mirrors constituting a resonator, i.e. an output mirror or a rear mirror as an optical component of the laser oscillator. The mirror 4 as the optical component is held by a retaining mechanism 8. The electric discharge tube 2 is arranged between the resonator mirrors, one of which is shown in FIG. 4, and incorporated in a circulating path including a blower. The gas laser medium 7 flows in the electric discharge tube 2 through the circulating path at high speed.
When the gas laser medium is pumped by electric discharge 3 generated in the electric discharge tube 2, stimulated emission light is amplified in the resonator and outputted from the output mirror (one of the resonator mirrors 4) according to known principle. In an operation of the laser oscillator, vaporized organic matter such as oil mist is mixed in ambience, i.e. gas laser medium in this example, of the optical component 4. In general, the optical component 4 is forcedly cooled through the retaining mechanism 8 for preventing distortion of the optical component 4 by heat.
The vaporized organic matter is cooled by the optical component 4 and congealed and adhered to surfaces of the optical component 4. Further, a gas stagnation 13 is caused between the optical component 4 and an inlet/outlet of the gas medium into/from the electric discharge tube 2 in the circulating path, to accelerate the congeal and adhesion of the organic matter on the optical component 4. Therefore, it is necessary to often lean the optical component 4 or change the optical component 4 with a new one to cause increase of running cost.
In Japanese Patent Publication No. 2001-284685A, there is described a laser oscillator in which a photocatalytic layer is arranged at inner walls of a casing of the laser oscillator. This technique relates to suppressing of deterioration of composition of gas laser medium by inorganic matter produced by chemical reaction in a gas laser oscillator. Organic matter such as oil mist contained as minor component in a large mount of gas laser medium circulating at high speed hardly react with the photocatalytic layer, so that the organic matter which contaminates the optical component is not effectively decomposed and removed. Further, since the phtocatalytic layer is arranged remote from the optical component, the phtocatalytic layer is scarcely expected to have a function of cleaning the optical component.